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20 A I R C R A F T E N G E N E E R I N G January, 1944 Translation s Issued by the N.A.C.A. coefficient at high speed must be computed with the VDI-Zeitschrift, Vol. 64, No . 18, 4 May, 1940. Technical Memorandum No. 1043. Ex sam e equation as a t low speed, when i t is referred to (Translation No. 104 of the David W. Taylor perimental Investigation of a Model of a Two- th e difference oi th e wall temperatur e of th e heated Model Basin, Bureau of Ships, Navy Dept., Stage Turboblower. By S. Dovjik and W. plat e in respect to its " natural temperature". Since this fact follows from the linear structure of Washington.) Pohkovsky. (Report No. 191 of the Central th e differential equation describing th e temperature Aero-Hydrodynamical Institute, Moscow, On the premise that the majority of structures field, it is equally applicable t o th e heat transfer in or structural units which are subjected to repeated 1935.) th e turbulent boundary layer. or fatigue stresses will, during their useful lives, be. An investigation is mad e of tw o stapes of a multi subjected to relatively few cycles of stress equal to stag e turbo-blower having a vanelcs s diffuscr behind thei r endurance limits and to still fewer cycles of th e impeller and guide vanes a t th e inlet to th e next Technical Memorandum No. 1046. Ex stress appreciably exceeding the endurance limit, stage . The method employed was tha t of investi perimental Investigation of Impact in Landing i t would be a waste of material and would produce gatin g th e performance of th e successive elements of unnecessarily heavy structures to base their design on Water. By R. L. Rreps. (Report No. 438, th e blower (the impeller, vanelcss diffuscr, etc.) on endurance-limit stresses, i.e., on the assumption whereb y the kinematics of the flow through the of the Central Aero-Hydrodynamical Institute, of a n unlimited numbe r of full load cycles. Further blower could be followed and the pressure a t the Moscow, 1939.) more, since the majority of machines which are different points computed. The character of the subjected to repeated stresses are not in constant Th e extent of agreement of th e theoretical impact flow and the physical significance of the loss co use, th e period ol rest might possibly prove "bene computation s with the actuai phenomenon ha s not efficients could thereby be determined so as to ficial t o their resistance to repeated stress. as ye t been fully clarified. There is on th e one han d secure the best agreement of the computed with a certain imperfection in th e theory (due t o simpli An extensive series of test s wa s mad e t o determine th e actual performance of the blower. Since the fying assumptions made) and on the other an in th e effect of rest periods on th e numbe r of cycles of test s were carried out for various delivery volumes sufficiency in th e experimental data available. The stress t o failure. The materials used for these tests th e dependence of the coefficients on a number of object of this paper is to show how far test results included one high-strength aluminium alloy, two factors (angle of attack, velocities, etc.) could be agree with the available approximate computation magnesiu m alloys, ingot iron, and two iron alloys, obtained . The distribution of th e losses tha t occur methods , t o investigat e in greate r detail th e physical pur e electrolytic copper, and brass; the chemical durin g the transformation of dynamic pressure at natur e of impact on water, and to perfect th e experi compositions are given in Table 1. Test specimens th e impeller exit into static pressure could b e found, menta l method of studying th e phenomenon. machine d from these materials were subjected to an d likewise the range within which the friction cycles of repeated tensile load in which the stress coefficient varies in th e vanelcss diffuscr. With the On th e basis of th e results obtained, th e following cycle varied between the limits of a small tensile aid of factors having a certain physical significance, conclusions may be drawn : stress, constant for a given material, and a larger th e centrifugal blower could be computed on the 1. The landing on wate r of a freely falling body is tensile stress. Figure 2 shows the shape of the basis of a more or less schematical consideration of determine d by two non-dimensional coefficients : magnesium specimens and the method of holding th e phenomena occurring during the air flow namely, th e Froud e numbe r an d th e mass coefficient. the m in the testing machine. throug h it, and the use of arbitrary factors and re Fo r th e case of a seaplane landing on water the im After determining the endurance limit and the course to the geometrical similitude law thus pac t phenomenon is determined by only the mass S-N diagram for a given material additional tests avoided. The present investigation largely sum coefficient. were made covering the same ranges of stress, but marizes all the previous work of the CAHI Blower in these additional tests th e specimen was permitted Section on the different elements of a centrifugal 2. The results obtained in computing th e impact t o res t withou t load for 6 t o 18 hours . These cycles blower. Some considerations on the analysis of b y the method of Wagner give a disagreement be of rest alternated with the cycles of stress, and in model test data for application to full-scale are tween th e compute d and th e tes t results in a number general there were from 7 t o 10 rest periods before presente d in the appendix. of cases. The added correction in the equation of failure of the specimens. Typical test results are motion for the weight of the body Mg, th e hydro given in Fig. 4 for th e Magnesium Alloy 2 specimen. stati c forces ySh, and the resistance of the water Th e conclusion to be drawn as a result of these kV» considerably improves the agreement of the Technical Memorandum No. 1044. Heat test s is that, in general, the rest periods had no theor y with th e tes t results. Transfer of Airfoils and Plates. By Otto effect on the number of cycles of a given range of 3 . An increase in the angle of a V shape (within stress required to produce failure. Seibert. (" Warmeubertragung von Profilen th e range of 5° to 30°) considerably decreases the Th e anomalous behaviour of the specimens of und Platten." Jahrbuch 1928 der deutschen velocity change on impact. ingot iron (Material 4) is, perhaps, the most in LuftschenLuftfahrtforschung,pp. II245-II256.) terestin g result of the report. For this material, teste d under repeated tensile loads wit h a minimum Th e few available test data on th e heat dissipa Technical Memorandum No. 1049. Re stress of 10 kg/mm s (14,225 pound s pe r square inch), tion of wholly or partly heated aerofoil models are searches on Preliminary Chemical Reactions in compared with the corresponding data for the flat failure occurred in some of the specimens a t a rela Spark-Ignition Engines. By E. Muhlner. plat e as obtained by an extension of Prandtl's tively small number of cycles; instead of under momentu m theory, with differentiation between going th e usual fracture without appreciable elonga (Luftfahrtforschung, Vol. 19, No . 18, Aug. 20, lamina r and turbulent boundary layer and tran tion these specimens elongated and necked down as 1942, pp. 249-266. R.T.P. Translation No. is usual for static tests. The explanation for this sitional region betwee n both, th e exten t and appear actio n is not apparent. When similar specimens ance of which depend upon certain critical factors. 1681. Issued by the Ministry of Aircraft were tested under cycles of stress in which rest Th e satisfactory agreement obtained justifies far- Production.) periods alternated with stress cycles, necking down reaching conclusions in respect to other profile Chemical reactions can demonstrably occur in a did not occur and no specimens failed at stresses forms and arrangements of heated surface areas. fuel-air mixture compressed in th e working cylinder u p to 29 kg/mm2 (41,250 pounds per square inch). Th e temperature relationship of th e material quan of an Otto-cycle (spark ignition) internal-com I n these cases th e endurance limit was a t about 94 tities in its effect on the heat dissipation is dis bustio n engine even before th e charge is ignited by pe r cent of the static tensile strength. Work- cussed as far as is possible at the present state of th e flame proceeding from th e sparking plug. These hardenin g and age-hardening appear to be factors research, and it is shown tha t the profile drag of ar e the so-called " preliminary reactions " (" prc- heate d wing surfaces can increase or decrease with in this behaviour, bu t th e test s were too few to per flame " combustion or oxidation), and an exact th e temperature increase depending upon the mi t definite conclusions. knowledge of their characteristic development is of momentaril y existent structure of the boundary I n Appendix 1 is a brief discussion of French's grea t importance for a correct appreciation' of the layer. " probable damage line" as given in Moore's phenomen a of engine-knock (detonation), and con Materials of Engineering. sequentl y for its avoidance. Such reactions can be I n Appendix 2 is a translation of the meaning of studied either in a working engine cylinder or in a th e expression "Time-Strength" as used in Ger Mechnical Memorandum No . 1045. Th e Heat combustio n bomb. The first method necessitates a many . There is no exact English equivalent al Transfer to a Plate in Flow at High Speed. complicated experimental technique, while the thoug h fatigue-strength at a specified number of second has the disadvantage of enabling only, a By E. Eckert and O. Drewitz. (" Der Warme- cycles for failure is often used with the same mean single reaction to be studied at one time. Conse ubergang an eine mit grosser Geschwindigkeit ing. quently , a new series of experiments was inaugur I n Appendix 3 is a description of the pulsating langs angestromte Platte. Forschung, Vol. n , ated , conducted in a motored (externally-driven) typ e of testing machine used for these tests . No. 3, May-June, 1940, pp. 116-124.) txj*i!;vrctfiv&?A «vgV»& ^ i ■mixta^-tom^wsavML type, withou t ignition, the resulting preliminary re Th e hea t transfer in th e lamina r boundar y laye r of action s being detectable and measurable thermo- a heate d plate in flow a t high speed can be obtaine d by metrically . integratio n of th e conventional differential equations of th e boundar y layer, so long as th e material values These . Technical Memoranda are not put on ca n be regarded as constant. This premise is fairly sale but can only be obtained by direct application The Effect of Rest Periods on the Time and well satisfied at speeds up to about twice the sonic to the Secretary, National Advisory Committee speed' an d at not excessive temperature rise of the Fatigue Strengths of Metallic Materials. By for Aeronautics, Washington, D.C., U.S.A. The heate d plate. The general solution of th e equation F . Bollenrath and H. Cornelius. ("Der Editor will, however, be glad to lend his personal includes Pohlhauscn's specific cases of hea t transfer einfluss von Betriebspausen auf die zeit- und copy of any of them to any reader who may wish t o a plate a t low speeds and of the plate thermo to borrow U for a few days for consultation. Dauerfestigkeit Metallischer Werkstoffe." meter . The solution shows tha t the heat transfer
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Jan 1, 1944
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